It is currently provided that two wireless terminals, examples of which according to several modern communications standards are referred to as a number of User Equipment (UE) can communicate with one another directly by means of D2D communication, and which of course is provided in addition to normal network connectivity. It has been suggested that valuable services could be provided by Third Generation Partnership Project (3GPP) wireless communication systems based on UEs being in proximity to each other. Such services could include Public Safety services and non-Public-Safety services that potentially would be of interest to operators and users.
For example, 3GPP technical report RP-122009, by Huawei and HiSilicon is entitled “Evaluation requirements for D2D”, 3GPP publication FS_ProSe, TR 22.803, and SP-120456-MoU between TETRA & Critical Communications Association (TCCA) & the National Public Safety Telecommunications Council), and S1-121247 (TCCA).
Also, 3GPP publication R1-130133 (ZTE—“Evaluation methodology for D2D discovery”) proposes that D2D-based proximity services (D2D ProSe) could be realized within or without 3GPP Long-term Evolution (LTE) network coverage, and in both cases detection signals would be used by UEs for D2D proximity direct discovery without position information.
There is currently a need for improvements relating to three technical aspects of D2D communications: discovery; D2D communication and signalling (including PHY and MAC layers, control layer and protocol design); and mitigation of the effects of noise and interference. Discussions below are concerned mainly with the last two of these technical aspects.
The physical environment in which wireless communication terminals are located changes over time. This can be due to changes in position, interference from other base stations or other terminals, power of received signals, distance between terminals, multipath attenuation etc. Also, D2D communication may affect cellular communication by interference of a signal used in the direct (D2D) communication link with signal(s) used in the cellular communication; and/or a D2D communication link may affect other D2D communication links by interference of a signal used in the direct (D2D) communication link with signal(s) used in such other D2D communication links.
Currently, the direct link (D2D link) between two terminals is established and maintained by means of signals transmitted between the two terminals and control of the quality of the direct link between the terminals is disadvantageously limited.
The present invention seeks to provide for wireless communications methods and related communications systems and terminal devices having advantages over known such methods, systems and terminals.